1. Technical Field
The present invention relates to a method for producing a composition for injection molding and a composition for injection molding.
2. Related Art
A powder metallurgy process for producing a metal product by sintering a molded body containing a metal powder has been widely used in many industrial fields recently because a near net shape sintered compact can be obtained using the process. Further, a ceramic powder can be used in place of a metal powder. There are many methods for producing a molded body (molding methods), and a powder injection molding method in which an inorganic powder and an organic binder are mixed and kneaded, and injection molding is performed using the resulting kneaded material (compound) is known. A molded body produced by such a powder injection molding method is then subjected to a degreasing treatment to remove the organic binder, followed by firing, whereby a metal product or a ceramic product in a desired shape is obtained.
In such a powder injection molding method, first, a metal powder and an organic binder are kneaded to obtain a kneaded material (see, for example, JP-A-11-131103). Then, the obtained kneaded material is subjected to injection molding, and the resulting molded body is degreased and fired, whereby a sintered compact is obtained.
However, in the case where the particle diameter of the organic binder powder is larger than that of the metal powder, it takes considerable time to uniformly mix these powders, and the temperature of the kneaded material is increased by self-heating, and the organic binder is decomposed due to the heat, resulting in the deterioration of the original function of the organic binder.
Further, a resin material to be used as the organic binder has significantly different properties from those of the metal powder, and therefore, both powders are easily separated from each other and the resin material and the metal powder are liable to be unevenly distributed in the composition. Due to this, even if a molded body is obtained by molding the obtained composition for injection molding, a problem of shape retainability such as low dimensional accuracy occurs.